1. Field of the Invention
The present invention relates to a volume control apparatus.
2. Description of the Related Art
In audio amplifiers, when an analog audio signal is input into a DSP, in the DSP, (1) a volume is controlled to a first volume level by a first volume controller, (2) the analog audio signal is converted into a digital audio signal by an analog-digital converter, (3) the digital audio signal is subject to a signal process, (4) a volume is controlled to a second volume level by a second volume controller, and the signal is output to an amplifier. When a sensitivity is set to 2 V, the volume level of the first volume controller is set to −6 dB. This is because since a maximum input voltage of the analog-digital converter in the DSP is 1 V, an analog audio signal of 2 V is reduced to 1 V so as to be input into the analog-digital converter. At this time, since the volume level of the first volume controller is set to −6 dB, the volume level cannot be sufficiently increased for the analog audio signal of 1 V. On the other hand, when the sensitivity is set to 1 V, since the analog audio signal of 1 V can be input directly into the analog-digital converter, the volume level of the first volume controller is set to 0 V. As a result, the volume level can be sufficiently adjusted for the analog audio signal of 1 V. At this time, overflow occurs in the analog audio signal of 2 V, and a noise is generated. In order to solve this problem, conventional audio amplifiers employ a function for manually controlling a sensitivity by means of a user's operation according to an analog audio signal to be input, but it is very complicated that the sensitivity is adjusted by a user's operation.